FMCW LiDAR Distance Calibration for Doppler Shift Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing distance measurement apparatuses fail to accurately calibrate distances due to Doppler shift errors when scanning a surface at rest with laser light, particularly when the optical axis is not perpendicular to the surface and a component of the measurement head's movement is in the same direction as the laser light's propagation.
Innovation Solution
A distance calibration device and method that utilizes a frequency-modulated continuous-wave (FMCW) LiDAR to scan a surface at rest, acquiring multiple distances and time points to calculate and correct for Doppler shift errors by using expressions involving distance and time differences, wavelength, and beat frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the surface of the measurement object is scanned at high speed with laser light, then the measurement speed is improved, but the measurement accuracy is degraded due to Doppler shift
Solution Approach 1:
The patent applies feedback by using the Doppler shift information obtained from the beat frequency to correct the distance measurement. The system continuously monitors the beat frequency between the transmitted laser light and the reflected light, calculates the Doppler shift, and uses this feedback to compensate for the measurement error, thereby maintaining high accuracy even at high scanning speeds
Solution Approach 2:
The patent changes the parameter approach by introducing a new correction parameter (Doppler shift compensation value) to the distance measurement calculation. Instead of simply measuring distance based on beat frequency, the system adjusts the measurement by adding the calculated Doppler shift compensation, effectively transforming the measurement process to account for the high-speed scanning effect
2Adaptability or versatility
If the optical axis of the measurement head is not perpendicular to the surface of the measurement object, then the measurement can be performed at oblique angles, but Doppler shift error increases
Solution Approach 1:
The system uses feedback from the beat frequency measurement to detect and correct Doppler shift errors. By continuously monitoring the frequency difference between transmitted and received light, the system can identify when oblique angle measurement causes Doppler shift and apply compensation, allowing versatile angular measurement while maintaining precision
Solution Approach 2:
The patent introduces an intermediary correction mechanism that mediates between the oblique measurement geometry and the distance calculation. The Doppler shift compensation acts as an intermediary factor that translates the geometric disadvantage into an accurate measurement by adjusting the raw distance value
3Adaptability or versatility
If the measurement head moves in the same direction as the laser light propagation, then the Doppler shift occurs, but this enables relative velocity measurement capability
Solution Approach 1:
The patent makes the system multi-functional by using the same FMCW LiDAR setup to achieve both distance measurement and relative velocity measurement. The beat frequency signal contains information about both the distance and the Doppler shift, allowing the system to extract multiple parameters from a single measurement process, thereby enabling velocity detection without sacrificing distance accuracy
Solution Approach 2:
The system uses feedback from the beat frequency to separate the distance and velocity information. By analyzing the frequency shift pattern, the system can determine the Doppler component and use it to correct the distance measurement, simultaneously enabling both precise distance measurement and relative velocity detection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate distance calibration by removing Doppler shift-induced errors, thereby enhancing the precision of distance measurements.
Implementation Method 1
there is a problem in that measurement accuracy is degraded due to a Doppler shift of light
Implementation Method 2
a relationship in distance between the measurement point and the measurement head is not changed
Data Source
AI summary
A distance calibration device and a distance calibration method are used for calibrating distances to measurement points on a surface of a measurement object, which are acquired by rotating laser light emitted from a measurement head of an FMCW LiDAR to scan the surface of the measurement object at rest. A first distance to a first measurement point among the measurement points, a second distance to a second measurement point in a vicinity of the first measurement point, and a first time point and a second time point at the first distance and the second distance are acquired. A Doppler shift is calculated based on the first distance and the second distance, the first time point and the second time point, and a wavelength of the laser light, a measurement error caused by the Doppler Shift is calculated, and the first distance is calibrated based on the calculated measurement error.